gro: reset vlan_tci on reuse

This one liner is part of upstream
commit 3701e513
Author: Jesse Gross <jesse@nicira.com>

    vlan: Centralize handling of hardware acceleration.

The bulk of that commit is a rework of the hardware assisted vlan tagging
driver interface, and as such doesn't classify for -stable inclusion. The fix
that is needed is a part of that commit but can work independently of the
rest.

This patch can avoid panics on the 2.6.32.y -stable kernels and is in the same
spirit as mainline commits
66c46d74 gro: Reset dev pointer on reuse
6d152e23 gro: reset skb_iif on reuse
which are already in -stable.

For drivers using the vlan_gro_frags() interface, a packet with an invalid tci
leads to GRO_DROP and napi_reuse_skb(). The skb has to be sanitized before
being reused or we may send an skb with an invalid vlan_tci field up the stack
where it is not expected.
Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Cc: Jesse Gross <jesse@nicira.com>
Acked-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -2614,6 +2614,7 @@ void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
 {
 	__skb_pull(skb, skb_headlen(skb));
 	skb_reserve(skb, NET_IP_ALIGN - skb_headroom(skb));
+	skb->vlan_tci = 0;
 	skb->dev = napi->dev;
 	skb->iif = 0;